PLANT LIFE. 



PART I: THE PLANT BODY. 



INTRODUCTION. 



1. Units of structure. An examination of any plant by 

 proper methods reveals the fact that it is made up of one or 

 more units of structure. The unit of structure of a brick 

 wall is the individual brick. Each has a definite shape and 

 relation to others, upon which the form of the wall depends. 

 The unit of structure of a plant is called a cell. The cells 

 have each a definite form and relation to others, and upon 

 these two factors the form of the entire plant depends. 



But between the plant and the brick wall there is this im- 

 portant difference. The bricks, after being perfectly formed, 

 were put together. The cells of the plant are produced where 

 they lie and gradually grow to a mature form and size. The 

 bricks are originally disconnected ; the plant-cells are con- 

 nected by origin, and only as they become mature do they 

 separate, if at all. 



2. The cell. A plant-cell is a minute portion of living 

 matter, called protoplasm or plasma, generally surrounded by 

 a membrane, called the cell-wall (fig. i). If the brick in 

 the previous illustration be taken to represent the protoplasm, 

 the mortar may be considered as the cell-Wall.* 



* This illustration must be carried no further than to show the relation 

 of position of these two parts of a cell. 



